This invention relates to a method for surveillance of the nuclear fuel in fuel elements and fuel bundles to detect any diversion of the nuclear material therefrom.
Typically nuclear fuel, such as uranium or plutonium oxide, is in the form of pellets or powder contained in a suitable container such as an elongated cladding tube sealed by end plugs to form a fuel element as shown, for example, in U.S. Pat. No. 3,378,458.
As typically used in a nuclear reactor core, a number of fuel elements are supported in spaced array between upper and lower tie plates to form a separately replaceable fuel assembly or bundle as shown, for example, in U.S. Pat. No. 3,689,358. A sufficient number of such fuel bundles are arranged in a matrix, approximating a right circular cylinder, to form the nuclear reactor core capable of self-sustained fission reaction. Periodically the core is refueled by replacement of some of the fuel bundles to restore the necessary reactivity. Thus the fuel bundle is the normal unit of fuel material transfer and use throughout the fuel cycle. That is, the fuel elements are assembled into bundles at the fuel fabrication factory. The bundles are shipped to the reactor and placed in the core. Eventually the bundles are removed from the core and stored as such or are shipped to a reprocessing plant.
An object of this invention is to provide a method and apparatus for obtaining a unique indication or signature of individual fuel elements and individual fuel bundles at any point in the fuel cycle to assure that the fuel material therein has not been removed or otherwise tampered with. Another object is to provide nondestructive surveillance of nuclear fuel elements and bundles.